1. Field of the Invention
This invention relates to an optical control arrangement having particular application in television or still video cameras and, more particularly, to the use of fuzzy inference, or fuzzy reasoning, to achieve highly accurate control.
2. Description of the Prior Art
Aperture control has been used in television cameras whereby a controllable diaphragm is adjusted automatically and/or in response to manual selection to regulate the amount of light passing therethrough and, thus, to regulate the brightness of an image focused onto a pickup element. Illustrative diaphragm adjustment techniques are described in Japanese Patent Applications Nos. 63-208825, 63-213098 and 63-215858. A typical prior art diaphragm control arrangement is illustrated in FIG. 1 herein.
As shown in FIG. 1, a diaphragm of blade-like construction is driven by an iris motor 2 in response to control signals produced by a diaphragm control circuit. The actual position or aperture of the diaphragm is detected by a Hall element 3; and the position indication produced by that element is compared to a desired position indication to determine whether the aperture should be increased or decreased. The desired position of the diaphragm, that is, the desired aperture opening, may be manually selected and a reference voltage V.sub.REF generated by a reference voltage generator 7 represents the desired diaphragm position. Typically, V.sub.REF is produced by an adjustable resistor or other variable voltage generator to represent the aperture opening desired by, for example, a television cameraman.
A voltage V.sub.K produced by Hall element 3 and representing the actual position of the diaphragm, is compared to the reference voltage V.sub.REF by resistors 4 and 5. The difference between these voltages, that is, the difference between the actual and desired positions of the diaphragm, is coupled to the inverting input of an integrating operational amplifier 10 via a resistor 6. The integrating operational amplifier is provided with a parallel RC circuit formed of resistor 11 and capacitor 12 connected in feedback relationship between the output terminal and the inverting input thereof. The integrated signal produced by amplifier 10 is supplied as a drive signal to a driving coil 13 of iris motor 2.
Operational amplifier 0 also includes a non-inverting input to which is supplied a standard voltage generated by a reference source 16 (schematically illustrated as a battery) and supplied through a resistor 14. A damping coil 18 included in iris motor 2 is coupled across the inverting and non-inverting inputs of this operational amplifier.
The drive signal supplied to driving coil 13 by operational amplifier 10 also is supplied by a resistor 21 to the inverting input of an integrating operational amplifier 20. Similar to operational amplifier 10, amplifier 20 is provided with a parallel RC circuit formed of resistor 24 and capacitor 22 connected in feedback relationship between the output terminal of operational amplifier 20 and the inverting input thereof. Amplifier 20 includes a non-inverting input supplied via a resistor 26 with the standard voltage produced by reference source 16.
Driving coil 13 of iris motor 2 is connected across the output terminals of integrating operational amplifiers 10 and 20, as shown. Accordingly, the iris motor is driven in a direction such that the actual position of the diaphragm, as represented by output voltage V.sub.K produced by Hall element 3, coincides with the desired position represented by the reference voltage V.sub.REF generated by reference voltage generator 7.
The prior art arrangement shown in FIG. 1 is subject to errors when the operating characteristics of, for example, the iris motor, differs from one television camera to another. Likewise, changes in temperature affect the operation of the illustrated arrangement in a manner which may not be fully predictable. Still further, since the mechanical tolerances between the iris motor, the Hall element and the diaphragm controlled by the motor may vary from one camera to another, it is difficult to realize an accurate computer model of the diaphragm control assembly.
Another disadvantage associated with the prior art arrangement shown in FIG. 1 resides in the non-linear relationship between the diaphragm aperture and the amount of light, or brightness of the image projected therethrough to an optical pickup. Although the diaphragm is adjusted in a generally linear manner by the illustrated arrangement, the optoelectric conversion characteristic of a typical pickup element used to generate a video siqnal in response to the image projected thereon is non-linear. Furthermore, the brightness of the optical image is logarithmically related to the level of the video pickup signal. That is, changes in the pickup signal level vary logarithmically with changes in the image brightness. Consequently, diaphragm adjustments may not be made quickly, smoothly and precisely when a user selects a new aperture opening.
In addition to effecting electronic aperture control in response to a manual adjustment, prior art television cameras (as well as still video cameras) include arrangements adapted to provide automatic focusing in response to a high frequency component of a video pickup signal. Such automatic focusing is described in Japanese Patent Application No. 63-215850.
When a television camera is properly focused, the boundary between a focused object and, for example, its background, is relatively sharp. Such a sharply defined boundary results in a high frequency component of the pickup signal produced by a pickup element onto which the focused object is imaged. The sharpness of this boundary is reduced when the object is out of focus. Thus, an indication of the focus condition of the television camera is provided by the high frequency component of the image pickup signal. Typically, the high frequency component is converted to a digital signal and processed in accordance with one or more predetermined algorithms to generate a control signal for automatically adjusting the focus condition of the camera.
The algorithms used to generate the focus control signal should take into account the possibility of a change in the high frequency component of the image pickup signal due to factors other than an out-of-focus condition, such as a signal level change due to movement of the subject, jiggling of the camera, and the like. Additionally, the algorithms should take into account the desirability of providing a very small change in the focus condition for the purpose of determining the direction in which focus correction must be made. Still further, additional algorithms are needed to prevent a change in the focus condition in the event that an object other than the desired subject moves through the imaging field, and particularly moves adjacent to or in front of the desired subject.
Thus, the control circuitry needed for automatic focusing is expected to be relatively complicated, thus adding to the overall complexity of the television camera. Also, even though many algorithms may be provided, such as mentioned above, supplemental algorithms generally are necessary to provide automatic focusing for a subject located in different environments. Hence, it is quite difficult, if not impossible, to provide a computer model for each anticipated environment. As a result, precise automatic focusing by use of such prior art techniques is not easily attainable.
Other television or still video camera optical controlling arrangements are used to adjust the aperture opening of the camera diaphragm in response to the brightness level of the signal produced by the pickup element included therein. This automatic diaphragm adjustment arrangement operates in conjunction with automatic gain control of the image pickup signal. Consequently, imaging in low light conditions can be achieved by providing a large aperture opening together with high signal gain.
For example, if the image pickup element is provided with a pickup screen M having a central portion MM, such as shown in FIG. 2, the brightness level of the image pickup signal produced by the central portion MM typically is assigned high priority (sometimes referred to as center-weighted priority). Aperture control as well as signal gain control are effected by detecting the signal levels derived from the higher priority central portion MM and from the lower priority peripheral portion of the pickup screen. For example, let it be assumed that the signal level averaged over central portion MM is represented as K.sub.MM and the signal level averaged over the peripheral portion of pickup screen M is represented as K.sub.MS. The weighted average of the overall signal derived from pickup screen M then may be expressed as K=2K.sub.MM +K.sub.MS. The aperture opening of the diaphragm is controlled such that K is made equal to a predetermined value. The influence over the aperture opening due to the central portion MM is seen to be greater than that due to the peripheral portion of the pickup screen.
In this type of automatic diaphragm control, automatic gain control over the image pickup signal also is provided so that, for example, when the image pickup signal level is low even though the diaphragm is fully opened, the signal gain is increased. Conversely, if the image pickup signal level is quite high even though the diaphragm opening is small, the signal gain is reduced. It is appreciated that there is a cooperative relationship between the level of the image pickup signal, the gain applied to that signal and the aperture opening of the diaphragm.
However, certain disadvantages are associated with the automatic aperture control arrangement of the aforementioned type. For example, if the pickup signal gain is changed and thereafter the intensity of the object imaged onto the pickup screen changes, a false or inadequate diaphragm adjustment may result. Also, movement of a bright object from central portion MM to the peripheral portion of pickup screen M will result in a sharp change in the weighted average of the overall brightness imaged onto the pickup screen that may cause an insufficient or incorrect diaphragm adjustment. Still further, when the television camera incorporating the automatic diaphragm adjustment arrangement is used in different environments, such as on snow, at the seashore, and the like, substantial brightness levels in the background may cause such a small aperture opening and small signal gain as to render the level of the pickup signal inadequate.